Problem: In physics class, the girl to boy ratio is $8$ to $10$. If there are a total of $54$ students, how many boys are there?
Answer: A ratio of $8$ girls to $10$ boys means that a set of $18$ students will have $8$ girls and $10$ boys. A class of $54$ students has $3$ sets of $18$ students. Because we know that there are $10$ boys in each set of $18$ students, the class must have $3$ groups of $10$ boys each. There is a total of $30$ boys in physics class.